The Spouse and I saw this on opening night a couple of weeks ago (the first time I've seen a movie on opening night since Serenity). I carefully hadn't re-read the book, so I could go in with a fairly blank slate.
Quick Summary: We really enjoyed the movie. You should see it. Probably not good for kids under, say, 8, but a lot of adults seem to think it'd be terrifying for all kids, while I think most kids are a lot more resilient than adults give them credit for. Your mileage, of course, may vary.
Gory details (no intentional spoilers):
The stop-motion animation is stunning and often beautiful. The 3-D effects (for the 3-D version, obviously) were mostly subtle and served the story, rather than vice-versa (I'm looking at you, Robert Zemeckis); there was only one moment out of the whole movie the 3-D-ness made me queasy.
The voice characterizations were very good. Dakota Fanning actually sounded like she was from the upper midwest (her family is supposed to be from Michigan, having just moved to suburban/rural Ashland, Oregon). John Hodgman (as the Dad/Other Dad) was entertaining without being distracting (I'm looking at you, Battlestar Galactica), and Teri Hatcher did a great job as the Mother/Other Mother.
Then there's the casting of Keith David as the voice of The Cat, Coraline's spirit guide (who in our world can't talk, but can in the Other World). Keith David is a fine actor, and on its own terms, this casting sort of worked, but it walked right into Magical Negro territory. I mean, really: a black cat with a deep, smooth African-American voice being a guide to a little white girl through a magical world full of danger? Please.
There were some changes from the book, some of which were fine (trimming some pieces back, making the Other Apartment and environs much brighter and more interesting); some were simply odd (removing the empty next-door flat that the "magic door" seemed to have opened into in the book); and some seem to have really pissed some people off (adding the neighbor boy, Wybie). The latter I understand; it can definitely be argued that it undercuts Coraline's independence, determination, and bravery in the last act (which in the book has her doing What Is Necessary entirely on her own). The one change I really didn't like was in the opening act, where Coraline's parents seem actively unpleasant, while in the book they were mostly distracted. Coraline also seems a year or two younger in the movie than she seemed to me in the book. Maybe that's simply a function of having to externalize her thought processes in a movie; in the book she seemed to have more of an interior life, with trenchant commentary on the foibles of adults — most of which would probably be unfilmable.
(One interesting bit is that Wybie, the added-for-the-movie neighbor boy, has no obvious signifiers that would make you think that he wasn't a suburban Oregon white kid, but his grandmother (who we meet at the end) is clearly black. This surprised or confused a lot of people, including the two black girls (and their mother) who sat behind us in the theater, so I feel fairly safe in thinking that I, a white boy from the suburbs, didn't miss anything obvious. Just for the record, Wybie is voiced by Robert Bailey Jr., who is in fact a young black man. This whole thing is neither here nor there, but coupled with the Black Cat issue, made me wonder how much of this was planned and how much was simply how things fell out.)
Bottom line: go see it. I'm really looking forward to the DVD, to see all the making-of documentaries.